Membrane/electrode assembly for polymer electrolyte fuel cell

Abstract

A membrane electrode assembly less susceptible to flooding or shortcircuiting caused by piercing of carbon fibers of a gas diffusion layer to a polymer electrolyte membrane is provided, containing a cathode having a catalyst layer and a gas diffusion layer, an anode having a catalyst layer and a gas diffusion layer, and a polymer electrolyte membrane interposed between the catalyst layer of the cathode and the catalyst layer of the anode, wherein each of the cathode and the anode further has a protective layer containing carbon fibers having an average fiber diameter of from 1 to 30 μm and a fluorinated ion exchange resin, between the catalyst layer and the gas diffusion layer, and the mass ratio (F/C) of the fluorinated ion exchange resin (F) to the carbon fibers (C) contained in the protective layer is from 0.05 to 0.30.

What is claimed is: 
     
       1. A membrane/electrode assembly for a polymer electrolyte fuel cell, comprising:
 a cathode having a catalyst layer and a gas diffusion layer, 
 an anode having a catalyst layer and a gas diffusion layer, and 
 a polymer electrolyte membrane interposed between the catalyst layer of the cathode and the catalyst layer of the anode, wherein 
 each of the cathode and the anode further has a protective layer comprising carbon fibers having an average fiber diameter of from 1 to 30 μm and a fluorinated ion exchange resin, between the catalyst layer and the gas diffusion layer, and 
 the mass ratio (F/C) of the fluorinated ion exchange resin (F) to the carbon fibers (C) contained in the protective layer is from 0.05 to 0.30. 
 
     
     
       2. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 1 , wherein the protective layer has a thickness of from 15 to 80 μm. 
     
     
       3. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 1 , wherein the fluorinated ion exchange resin contained in the protective layer has an ion exchange capacity of from 0.5 to 2.0 meq/g dry resin. 
     
     
       4. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 1 , wherein the fluorinated ion exchange resin contained in the protective layer is a perfluoropolymer having ion exchange groups. 
     
     
       5. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 1 , wherein at least one of the cathode and the anode further has a bond drainage layer comprising carbon fibers having an average fiber diameter of from 1 to 200 nm between the catalyst layer and the protective layer. 
     
     
       6. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 5 , wherein the bond drainage layer has a thickness of from 2 to 15 μm. 
     
     
       7. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 5 , wherein the bond drainage layer further contains a fluorinated ion exchange resin. 
     
     
       8. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 7 , wherein the mass ratio (f/c) of the fluorinated ion exchange resin (f) to the carbon fibers (c) contained in the bond drainage layer is from 0.05 to 2. 
     
     
       9. The membrane/electrode assembly for a polymer electrolyte fuel cell according to  claim 1 , wherein at least one of the cathode and the anode further has a microporous layer comprising carbon particles, between the protective layer and the gas diffusion layer.